Since the 1960s, researchers exploring the potential of artificially-structured materials for applications in quantum electronic devices have sought combinations of metals and semiconductors that could be combined on the nano-scale with atomically-sharp interfaces. Early work with multilayers of polycrystalline elemental metals and amorphous semiconductors showed promise in tunneling devices. More recently, similar metal/semiconductor multilayers have been utilized to demonstrate novel optical metamaterials. These metal/semiconductor multilayers, however, are not amenable to atomic-scale control of interfaces. We developed the first epitaxial metal/semiconductor multilayer and superlattice heterostructures that are free of extended defects. These rocksalt nitride superlattices have atomically sharp interfaces and properties that are tunable by alloying, doping and quantum size effects. Furthermore, these nitride superlattices exhibit exceptional mechanical hardness, chemical stability and thermal stability up to ~1000֩C.